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3D Survey and Documentation of an Early Iron Age Burial from Otzing, near Deggendorf in Lower Bavaria

1. Archaeological information about the Otzing project

An extraordinary find was made in the course of a rescue excavation carried out in 2010, in advance of construction of sport fields near Otzing in Lower Bavaria. The excavation revealed a spectacular burial site, located amongst Neolithic settlement pits and other badly preserved Early Iron Age (800–450 BC) burials that indicate an almost destroyed larger burial ground (for preliminary reports see Claßen et al. 2013; Gebhard 2014; Gebhard et al. 2015). The burial can be dated to the second half of the seventh century BC. The first indication of the burial in question was a circular ditch, 18.5 m in diameter, remaining from a former burial mound destroyed through later ploughing. A rectangular burial chamber, of about 13 m2, has come to light inside this ditch. The excavation of this feature began. Large quantities of pottery were discovered in the eastern part of the burial chamber. These are typical items to be found in Early Iron Age graves, likely to have been used for offerings of food and drinks. Animal bones detected near the vessels may have served the same purpose. A bronze cup was also found amongst the vessels. Bronze vessels are very rare in graves from this period. This find suggests the importance of the person buried at Otzing. This discovery was only the tip of an iceberg as subsequent finds, described below, have confirmed. While unearthing the central part of the chamber, where the actual burial was expected to be located, a wooden artefact came to light. It was richly decorated with bronze studs and subsequently identified as a yoke. Wooden parts in such burials are normally decayed, but this object was exceptionally well preserved in the central part of the chamber. The bronze decoration confirmed the assumption made earlier, based on the bronze cup, that the Otzing burial was an outstanding ensemble.

The excavation had to stop after this discovery due to the fragility of the wooden artefact. Further field excavation would have led to its destruction. Almost the entire burial chamber was subsequently block-lifted by the Archäologische Staatssammlung München (Bavarian State Archaeological Collection, Munich). Two large blocks were recovered and moved to the museum laboratories, alongside a smaller block. The large block was X-rayed to get an idea of its contents. The X-ray images showed the astonishing contents that has been visualised in the video below. The smaller block contained most of the pottery which was, to a large extent, already excavated. The large block, measuring 2.3 x 1.7 m, contained the entire central part of the burial chamber with the grave and the wooden yoke. The museum conservators excavated the two blocks as soon as they arrived at the laboratories. The investigation was generously supported by the Ernst von Siemens Foundation. Laboratory excavation benefits from a less tight schedule than fieldwork and can be performed with much greater care and precision. Therefore the observations and analyses of parts of the burials can normally be more detailed, resulting in substantial documentation. This leads to an insightful understanding of how the grave was erected and of the processes it has undergone, leading to its present state. The process was documented using both analogue and digital methods. Part of the documentation is the mapping of samples and observations using a Geographic Information System (GIS) with multiple documentation layers and 3D scans. Detailed analyses of stratigraphy and relationships can therefore be performed digitally. Furthermore, the 3D scanning of the large block and of individual items in the grave, will later become an important part of the museum display.

The large block contained a grave with the remains of a young man and a large number of goods. The deceased was laid on several pieces of wood extensively decorated with thousands of bronze studs. Pieces of similarly decorated leather were found amongst the wood. These parts might have been of furniture, possibly a wagon. Wagons are regularly found in ostentatious burials from the same period. They are interpreted as status symbols of the elite. Richly decorated horse gear and the yoke support a wagon hypothesis about this burial. The identification of the wooden object remains uncertain. It might have been a wagon, but it could also be a chair-like bier or some other furniture. In any case, the furniture along with the yoke and the horse gear hint of a burial of a member of the elite of the Early Iron Age. The decoration and the good state of preservation of these finds make them some of the most significant and beautiful examples ever recorded. Earlier excavations of similar finds often consisted of only some bronze studs. The goods discovered in the Otzing grave also include two spears and a dagger, tools, garment and toiletry articles. The leather belt of the dagger is decorated with bronze studs, making it a companion piece to the furniture. Bronze and probably iron pins were discovered on the chest of the deceased, alongside textile parts preserved of the garment in which the deceased was buried. The set of toiletry articles consists of three items that might have been worn around the neck, in a leather bag closed by a beautiful amber bead.

The discovery of Otzing is one of the most important finds in Bavaria in the last decades. Once preserved and exhibited, it will be a fascinating addition to the museum display and will offer unique insights into the burial ritual, material culture and the social structure of the period.

In order to support archaeological documentation and analysis, it was decided to digitally record the geometry and original colours of the surface of each excavation layer in detail and accurately. The original plan was to record up to three excavation layers over the time. Special individual finds, such as the yoke and dagger, were to be digitised with a higher level of detail in 3D and original colour.

The colour and 3D digitisation was divided into three steps for each excavation layer: First, the surface geometry of the grave was recorded in 3D using a fringe-projection system, considered an appropriate precision technology. Second, the colour of the surface was recorded in the visual spectrum. This was done using a commercial digital, single-lens reflex camera (DSLR). The digital images were processed using photogrammetric methods. Third, the data were integrated in a geographic information system (GIS) connected to a database.

2.2.1 Layered 3D digitisation of excavated phases

Three-dimensional digitisation was carried out with a fringe-projection system, an active stereo-photogrammetry technique. This technique offers the flexibility of the required 3D resolution and a high range of accuracy.

The number of individual scans is determined by various factors such as a high overlap between multiple scans, the detectable maximum area of a single scan, and finally by the object-specific shadings. The number of scans in 2015 was significantly higher than in 2012 and depended upon the complexity and fineness of the finds in the excavation layer.

Lateral scanner position with the acquired, corresponding surface area.

The combined colour and 3D data were the basis for visualisation of the Otzing find and its analysis. By using a GIS system (QGIS) these data (2.5D) could be used as basis for the archaeological documentation of the excavation steps having a link to a database. For such kind of analysis, it is not enough to use geometric data because they provide incomplete information on the object and a complete mapping of the excavation layer is not possible. In addition to the 3D data, a photogrammetric multi-image collection was created to provide detailed colour information. The "structure from motion" technique was used to fuse the the data.

Schematic workflow for fusion of 3D data and colour information from photographs.